This chapter speaks about a 75-year-old woman admitted with a 4-year history of progressive social withdrawal, decreased fluency, and difficulty handling complex tasks. Magnetic Resonance Imaging (MRI) of the brain showed prominent mesencephalic atrophy, dilation of the third ventricle, and mild cerebral atrophy. Based upon her history and examination, the patient met National Institute of Neurological Disorders and Stroke - Society for Progressive Supranuclear Palsy (NINDS-SPSP) diagnostic criteria for probable Progressive Supranuclear Palsy (PSP). Available data showed that the diagnosis of PSP was pathologically confirmed in essentially 100% of patients who meet these criteria. The patient's motor function progressively worsened, and she died from respiratory complications, approximately 6 years following symptom onset. Progressive supranuclear palsy is a sporadic neurodegenerative disease, which is defined clinicopathologically by the constellation of atypical parkinsonism, supranuclear vertical gaze palsy, and a characteristic pattern of tau accumulation within the brainstem and basal ganglia.

Diffusion-weighted MR imaging (DWI) is a technique in which microscopic water motion is responsible for the contrast within the image. Diffusion of water molecules alters conventional T1- and T2-weighted MR imaging, because it induces a signal dephasing and a signal loss. Clinical practice uses different representations of the results of DWI data processing: diffusion weighted images, DWI trace and ADC maps, which are all equivalent. DWI is more accurate than CT in localizing ischemic lesions shortly after stroke onset. DWI can show small lesions adjacent to the cerebrospinal fluid. The NINDS and ECASS studies have demonstrated an increased risk of hemorrhagic transformation in stroke patients with a large area of hypodensity on admission CT when treated with thrombolytic therapy. DWI affords accurate localization of strokes. Finally, DWI can more frequently differentiate a small deep subcortical infarct from a cortical or a combined cortical/subcortical lesion than conventional MR imaging can.